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Frequency Hopping, no danger of disturbance
Frequency-hopping or ‘frequency-hopping spread spectrum’ to give it its full title is basically a method of changing frequencies whilst communicating, to prevent the intrusion or interception by others – its a secure method of radio transmission. Spread spectrum has a huge number of applications in the communication technologies of today.

Wiki avoids naming the original inventor and patent holder because it has made contemptuous remarks about him in the past and true to form, grabs the nearest name of someone who just happened to be a physicist: “Perhaps the earliest mention of frequency hopping in the open literature is in radio pioneer Jonathan Zenneck’s book Wireless Telegraphy (German, 1908, English translation McGraw Hill, 1915), although Zenneck himself states that Telefunken had already tried it. https://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum#Multiple_inventors~
So where did Telefunken get the idea?

eetimes.com tells us of the things that Wiki ignores: “Nikola Tesla, the prolific Serbian-American inventor and radio pioneer, filed a U.S. patent, granted on March 17, 1903 which doesn’t mention the phrase “frequency hopping” directly, but certainly alludes to it. Entitled “Method of Signaling,” the patent describes a system that would enable radio communication “without any danger of the signals or messages begin disturbed, intercepted, interfered with in any way”.

Tesla’s patent details a system whereby transmitter and receiver are synchronized and hop between two channels (although the patent notes any number of channels could be used) by altering the carrier frequency in a predetermined sequence to avoid interference.

Such an interesting idea didn’t escape the military’s attention of course, and by 1915, the Germans were making use of primitive frequency hopping radio to stop the British eavesdropping on their conversations. If the British had done their homework, they could have found out the details of the technology by picking up a copy of Jonathan Zenneck’s book Wireless Telegraphy that was originally published in German in 1908, but translated into English the same year as the enemy started using frequency hopping on the front line.

Zenneck was a German physicist and electrical engineer who had got interested in radio by attending Tesla lectures on “wireless sciences”. Wireless Telegraphy includes a section on frequency hopping, and, as it became a standard text for many years, probably introduced the technology to a generation of engineers.[1]” http://www.eetimes.com/document.asp?doc_id=1279374

Nikola Tesla Guided Weapons & Computer Technology by Leland Anderson
In this, the third book of the Tesla Presents Series, engineer-historian Leland Anderson provides the transcript of the 1902 U.S. Patent Interference investigation concerning Tesla’s System of Signaling. The document, “Nikola Tesla vs. Reginald A. Fessenden,” which is no longer on file at the U.S. Patent Office, contains Tesla’s own depositions as well as those of his closest and most trusted associates, George Scherff and Fritz Lowenstein.

Included is material on the history of radio-controlled devices, the first practical form of these being Tesla’s radio-controlled “telautomaton” — an operational boat first demonstrated to the public at Madison Square Garden in 1898. In addition to describing Tesla’s “individualization” techniques for obtaining secure noninterferable radio communications—the patent is today recognized as the fundamental AND logic gate, a critical element of every digital computer—the interference record also reveals that essential features of the spread-spectrum telecommunications techniques known as frequency-hopping and frequency-division multiplexing have their roots in the resulting patents. Furthermore, there are new disclosures by Tesla on the operation of his large high voltage radio-frequency oscillators at both the Houston Street laboratory and the Colorado experimental station. Rarely in the history of science do we encounter such opportunities to gain deep insight into the fundamental ideas and concepts of an esteemed scientist/inventor.